BSc Third Year (Sem 5 & 6) Physics – Daily Revision MCQ (English Medium)
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A parallel-plate capacitor has capacitance C₀ in vacuum. If the space between its plates is completely filled with a dielectric of dielectric constant K, its capacitance becomes:
Chapter 2: Dielectrics
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Answer: C. KC₀
Filling the gap with a dielectric reduces the field between the plates by a factor K, so C = KC₀.What is the magnetic field at the centre of a circular loop of radius R carrying a steady current I?
Chapter 5: Magnetostatics
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Answer: B. μ₀I/(2R)
From the Biot–Savart law, every element of the loop adds μ₀I dl/(4πR²); summing over 2πR gives B = μ₀I/(2R).Lenz's law, which fixes the direction of the induced current, is a consequence of the law of conservation of:
Chapter 6: Electromagnetic Induction
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Answer: D. Energy
The induced current opposes the change causing it; otherwise current would be produced with no work done, violating conservation of energy.According to Maxwell's theory, the speed of electromagnetic waves in vacuum is given by:
Chapter 7: Maxwell's Equations and Electromagnetic Waves
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Answer: A. 1/√(μ₀ε₀)
Maxwell's equations give the wave equation with speed c = 1/√(μ₀ε₀) ≈ 3 × 10⁸ m/s, equal to the speed of light.When a ferromagnetic material is heated above its Curie temperature, it becomes:
Chapter 8: Magnetic Properties of Materials
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Answer: B. Paramagnetic
Above the Curie temperature thermal agitation destroys the alignment of domains, and the material behaves as a paramagnet (Curie–Weiss law).For a particle with energy E less than the barrier height V₀, the probability of tunnelling through a rectangular potential barrier increases when:
Chapter 15: Potential Step, Barrier and Quantum Tunnelling
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Answer: D. The barrier becomes narrower
Transmission falls roughly as e^(−2κa) with κ = √(2m(V₀−E))/ħ, so a smaller width a raises it, while larger V₀ or m lowers it.In Lagrangian mechanics, the Lagrangian L of a conservative system is defined as (T = kinetic energy, V = potential energy):
Chapter 16: Lagrangian Mechanics
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Answer: A. T − V
L = T − V; T + V is the total energy (the Hamiltonian for such systems), not the Lagrangian.For a particle moving under a central force, which quantity remains constant throughout the motion?
Chapter 17: Central Force Motion
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Answer: C. Angular momentum
A central force acts along the radius vector, so its torque about the centre is zero and angular momentum is conserved.The splitting of the sodium yellow line into the D₁ and D₂ doublet, even without any external field, is explained by:
Chapter 18: Atomic Spectra and the Vector Atom Model
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Answer: B. Spin–orbit interaction
Spin–orbit coupling splits the 3P level into 3P₁/₂ and 3P₃/₂; transitions from these to 3S₁/₂ give D₁ and D₂. Zeeman and Stark effects need external fields.In the pure rotational spectrum of a rigid diatomic molecule with rotational constant B (in cm⁻¹), adjacent lines are separated by:
Chapter 19: Molecular Spectra: Rotational and Vibrational
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Answer: D. 2B
Rotational terms are F(J) = BJ(J+1); with ΔJ = ±1 the lines lie at 2B(J+1), so successive lines are 2B apart.
BSc Third Year (Sem 5 & 6): MCQ in other subjects
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All questions are written by PadhaiNotes in our own words from the common syllabus of Maharashtra universities (NEP). Your own university's syllabus may differ a little.